In recent years, a lane mark recognition device is known wherein imaging means such as a CCD camera mounted on a vehicle picks up an image of a surface of the road on which the vehicle is traveling, and the picked-up image is processed to detect lane marks provided on the road for marking travel lanes. For the lane marks provided on the road, the following two types of lane marks are used: lane marks of a line type, such as a lane-marking line (white line); and lane marks of a stud type provided discretely, such as Botts Dots (Nonretroreflective Raised Pavement Markers) and a cat's eye (Retroreflective Raised Pavement Marker). Thus, there has been proposed a technique to accurately detect a plurality of shapes of lane marks by switching recognition algorithm in accordance with the shape of the lane mark (see, e.g., Japanese Patent Laid-Open No. 2003-317106 (hereinafter, referred to as “Patent Document 1”)).
The travel path recognition device of Patent Document 1 is provided with a straight-line detection processing unit that performs detection based on segment components of a picked-up image and a pattern matching processing unit that performs detection based on a pattern corresponding to the shape of the lane mark of a metal stud or the like, and it performs detection of the travel path based on a result of detection by either the straight-line detection processing unit or the pattern matching processing unit that is designated as means to be used for detection. In the state where one of the straight-line detection processing unit and the pattern matching processing unit is designated as the means to be used for detection, if it is no longer possible for the designated unit to detect the lane marks with accuracy, then the travel path recognition device switches the unit by designating the other unit as the means to be used for detection.
Meanwhile, the lane marks of similar shapes may have different colors, such as white lines and yellow lines. If they are different in color, even if they are similar in shape, it may be difficult to detect the lane marks using the same recognition algorithm. For example, the yellow line is lower in luminance than the white line, and has only a small difference in luminance with the road surface. Thus, the yellow line may not be recognized as a lane mark using the algorithm that detects a white line based on the luminance. Further, since the lane marks of different colors have different meanings in the road rules, it is desirable to appropriately recognize the lane marks of respective colors. With the device of Patent Document 1, however, the color of the lane mark is not taken into consideration upon recognition of the lane mark, which hinders appropriate recognition of the lane marks of different colors.